The present invention relates to a method of treating wastewater and a wastewater treatment equipment, in particular, for recycling reactants and unreacted chemicals to reduce genesis sludge capacity and consumption of chemicals.
In an era of reducing waste, various methods of reducing sludge generated in a wastewater treatment equipment are being studied.
Also, a method of treating wastewater of regenerating and recycling sludge generated from chemicals in use such as a coagulant and the like is being examined with the objective of reducing treatment costs.
For example, with regard to sludge containing unreacted chemicals, a method of reusing the unreacted chemicals is employed. The unreacted chemicals include unreacted calcium hydroxide, unreacted aluminium hydroxide and so on. When aluminium hydroxide sludge is generated, aluminium is eluted from the sludge to reuse the aluminium. These unreacted chemicals are reused for the purpose of reducing a genesis sludge capacity and consumption of chemicals.
FIG. 17 shows an example of these conventional wastewater treatment equipment. In this conventional equipment, wastewater flows into a first water tank 101 used as a raw water tank. After the wastewater stored in the first water tank 101 for a certain period of time, the wastewater is introduced into a conventional reaction tank 134 by a raw water pump 102.
This reaction tank 134 is provided with a rapid reaction tank agitator 105 and a pH meter 106. Returned sludge containing reactants and unreacted chemicals is introduced into the reaction tank 134 and an acid or alkali is added to the returned sludge. As a more specific example, returned sludge in a wastewater treatment equipment for treating fluorine contains aluminium fluoride as a reactant and aluminium hydroxide as an unreacted chemical. The pH in the reaction tank 134 needs to be eleven or higher to reliably elute aluminium from aluminium fluoride and aluminium hydroxide in the returned sludge.
However, a large amount of alkali such as calcium hydroxide or the like is required to adjust to pH 11 or higher in the reaction tank 134. Therefore, particularly when calcium hydroxide is added, not only running costs are increased since the consumption of chemicals added into the reaction tank is increased, but also sludge is generated by calcium hydroxide.
In general, poly aluminium chloride, aluminium sulfate or the like is excessively added as a coagulant in wastewater treatment. Therefore, various methods of regenerating and recycling the above aluminum compounds are being studied.
Such prior art includes the one disclosed in Japanese Patent Laid-Open Publication HEI 9-276875. This prior art is a method of treating wastewater for reducing the quantity of generated sludge and chemicals used for fluorine wastewater treatment. Specifically, aluminium sulfate is added to fluorine-containing wastewater as a coagulant to generate precipitates in a first reaction tank with pH 6.5. Subsequently, after the precipitates are separated by a precipitating tank, water and sulfuric acid are added to the precipitates in a separate second reaction tank and adjust to pH 4.0 so that coprecipitated fluorine is eluted. Then, after a solution containing fluorine is separated in a precipitating tank, the remaining precipitates are returned to the first reaction tank and recycled as a coagulant.
In these reactions, aluminium sulfate sludge is precipitated in a neutral region while containing fluorine and the fluorine is introduced from the precipitate (elution of fluorine) into an acidic or alkaline region. Aluminium sulfate is recycled as a coagulant containing no fluorine in the precipitate in the acidic or alkaline region. Consequently, the quantity of generated sludge and aluminium sulfate as a coagulant chemical are reduced by recycling aluminium sulfate.
Another prior art is disclosed in Japanese Patent Laid-Open Publication HEI 6-262170. In this prior art, after aluminium hydroxide is used to adsorb fluorine contained in wastewater in a first reaction tank, calcium chloride is allowed to act on fluorine-adsorbed aluminium hydroxide in a second reaction tank with pH 8. Subsequently, wastewater is introduced into a precipitating tank so as to allow calcium chloride to act on the fluorine-adsorbed aluminium hydroxide. Calcium fluoride formed thereby is precipitated and separated.
In a supernatant separated by this precipitation, aluminium hydroxide is regenerated to produce an aluminate solution. Furthermore, the aluminate becomes aluminium hydroxide by adjusting to pH 7 in a third separate reaction tank. Thus, aluminium hydroxide is regenerated as a coagulant. This aluminium hydroxide is returned to the first reaction tank and thus a recycling is completed. As a result of this prior art, the consumption of aluminum as a coagulant and the quantity of aluminium hydroxide sludge can be reduced.
Furthermore, another prior art is disclosed in Japanese Patent Laid-Open Publication HEI 9-19681. In this prior art, after fluorine contained in wastewater is adsorbed to aluminium hydroxide in the first reaction tank, wastewater is introduced into the precipitating tank to be separated into supernatant and aluminium hydroxide as precipitate. Subsequently, excessive calcium sulfate is added into a second separate reaction tank to generate calcium fluoride. Consequently, fluorine adsorbed to aluminium hydroxide is desorbed.
By fixing a surplus calcium ingredient as hardly soluble calcium sulfate, aluminium hydroxide is generated with a strong alkali in a third separate reaction tank (dissolving tank). This generated aluminium hydroxide is returned to the first reaction tank and thus a recycling is completed. As a result of this prior art, the consumption of aluminum as a coagulant and the quantity of aluminium hydroxide sludge can be reduced.
As shown in FIG. 17, a common reaction tank used in the above-described prior art is a usual water tank in which a rapid reaction tank agitator 105 and a pH meter 106 are installed in a conventional reaction tank 134.
First of all, it is required to solve problems related to a recycling in a conventional reaction tank 134 by constructing a reaction tank in which, for example, aluminium contained in returned sludge as an active ingredient is easily eluted and recycled.
In the above-described prior art disclosed in Japanese Patent Laid-Open Publication HEI 9-276875, 6-262170 and 9-19681, a reaction tank and a precipitating tank are required in any case when aluminium hydroxide is regenerated. Consequently, a problem arises that costs for constructing a system including equipment related to a reaction tank and a precipitating tank are high.
Specifically, for example, it is required to clarify conditions of regenerating aluminium hydroxide, aluminium fluoride or the like and examining the conditions in detail so that a wastewater treatment system achieving an object of regeneration can be constructed with little equipment investment.
Accordingly, an object of the present invention is to provide a method of treating wastewater and a wastewater treatment equipment with reduced waste at low cost and, furthermore, to provide a method of treating wastewater and a wastewater treatment equipment which can regenerate objective substances for use in wastewater treatment with little equipment investment.
In order to achieve the above object, the present invention provides a method of treating wastewater comprising the steps of: introducing wastewater into a reaction tank; introducing returned sludge into a separate reaction unit installed in the reaction tank to obtain a separate reactant by carrying out a separate reaction from a reaction in the reaction tank; and introducing the separate reactant from the separate reaction unit into the reaction tank.
According to this invention, a predetermined reaction is carried out in a reaction tank while a separate reaction is carried out in a separate reaction tank. Separate reactants generated from returned sludge by the separate reaction are introduced into the reaction tank and can be used for wastewater treatment in the reaction tank. Since the separate reaction tank is provided in the reaction tank, equipment investment costs can be minimized. Therefore, a method of treating wastewater with reduced waste can be achieved at low cost.
The present invention also provides a wastewater treatment equipment comprising: a reaction tank into which wastewater is introduced for reaction of the wastewater; and a separate reaction unit installed in the reaction tank, into which returned sludge is introduced, in which a separate reaction from a reaction in the reaction tank is carried out to obtain a separate reactant, and from which the separate reactant is introduced into the reaction tank.
According to this invention, the separate reaction unit is constituted in the reaction tank so as to carry out two separate reactions as a two-stage reaction. The reaction in the separate reaction unit generates a separate reactant from the returned sludge tank, and the separate reactant is directly introduced from the separate reaction unit into the reaction tank to be used for wastewater treatment in the reaction tank. Therefore, a wastewater treatment equipment with reduced waste can be produced at low cost.
In one embodiment of the invention, the separate reaction unit is an elution unit for eluting a chemical from reactants and unreacted chemicals contained in the returned sludge.
According to this embodiment, chemicals are eluted from the reactants and unreacted chemicals in the separate reaction unit, so that the eluted chemicals can be usefully recycled for wastewater treatment in the reaction tank. Aluminium fluoride and aluminium hydroxide can be mentioned as a specific example of reactants and unreacted chemicals, respectively.
In one embodiment of the invention, the reactants and the unreacted chemicals are substances derived from coagulants.
According to this embodiment, the unreacted chemicals derived from coagulants can be recycled to reduce the consumption of the coagulants. In general, a large amount of coagulant such as poly aluminium chloride is used for fluorine treatment in a fluorine wastewater treatment equipment.
In one embodiment of the invention, an acid or a alkali is added into the elution unit.
According to this embodiment, since an acid or alkali is added into the elution unit, chemicals are easily eluted from the reactants and unreacted chemicals by the acid or alkali. As a specific example, aluminum as an active ingredient is eluted by changing pH of aluminium fluoride as a reactant and aluminium hydroxide as an unreacted chemical.
In one embodiment of the invention, the returned sludge contains aluminium or iron.
According to this embodiment, aluminium or iron is eluted from the returned sludge so as to be recycled.
In one embodiment of the invention, the acid is a mineral acid and the alkali is calcium hydroxide or sodium hydroxide or both of them.
According to this embodiment, since the acid is a mineral acid such as sulfuric acid, hydrochloric acid or nitric acid, a wastewater treatment equipment can be easily constructed. Since the alkali is calcium hydroxide or sodium hydroxide or both of them, which are representative chemicals widely used, a wastewater treatment equipment can be easily constructed. It is generally known that when an acid is added to sludge, sludge is dissolved. That is, ingredients can be eluted by adding sulfuric acid, hydrochloric acid or nitric acid to sludge. Sludge ingredients can also be eluted by adding a alkali such as calcium hydroxide or sodium hydroxide to sludge. For example, it is typical that aluminium is eluted by adding calcium hydroxide to aluminium hydroxide sludge to raise the pH.
In one embodiment of the invention, the separate reaction unit is provided with an agitating means.
According to this embodiment, reaction efficiency in the reaction unit is improved by agitation with the agitating means.
In one embodiment of the invention, the agitating means of the separate reaction unit is a non-submersible agitator.
Since a non-submersible agitator is the most common type, a wastewater treatment equipment can be easily constructed.
In one embodiment of the invention, the agitating means of the separate reaction unit is a submersible agitator.
According to this embodiment, since a submersible agitator is installed in a water tank of the separate reaction unit, a wastewater treatment equipment can be constructed without making noise in a place with a strict noise regulation.
In one embodiment of the invention, the agitating means of the separate reaction unit is an agitating means by aeration.
According to this embodiment, since agitation in the separate reaction unit is performed by aeration, no noise is made and sludge can be loosened additionally.
In one embodiment of the invention, a pH meter is installed in the separate reaction unit.
According to this embodiment, since pH of the separate reaction unit can be sensed and recognized by the pH meter, optimal pH conditions for regeneration in the separate reaction unit can be recognized and set.
In one embodiment of the invention, the separate reaction unit is a line mixer.
According to this embodiment, the line mixer enables the inflow returned sludge and an acid or alkali to be physically agitated. That is, the returned sludge can be agitated without installing an agitating means such as an agitator or the like.
In one embodiment of the invention, the separate reaction unit is a cyclone.
According to this embodiment, the cyclone enables the inflow returned sludge and an acid or alkali to be physically agitated. That is, the returned sludge can be agitated without installing an agitating means such as an agitator or the like.
The present invention also provides a wastewater treatment equipment for treatment of fluorine wastewater, comprising: an acid raw water tank; a reaction tank; a poly aluminium chloride coagulating tank; a polymer coagulant coagulating tank; a precipitating tank; and an elution unit installed in the reaction tank, into which returned sludge from the precipitating tank is introduced, in which a separate reaction from a reaction in the reaction tank is carried out to elute a chemical from reactants and unreacted chemicals contained in the returned sludge, and from which the eluted chemical is introduced into the reaction tank.
According to this invention, an active ingredient in unreacted chemicals is eluted in the elution unit installed in the reaction tank and introduced into the reaction tank. While reusing this active ingredient, fluorine contained in wastewater can be treated.
The present invention further provides a wastewater treatment equipment for treatment of fluorine wastewater which contains hydrogen peroxide or organic matter, comprising: an acid raw water tank; a recycling tank having a precipitation section, to which returned sludge is introduced; a reaction tank; a poly aluminium chloride coagulating tank; a polymer coagulant coagulating tank; a precipitating tank; and an elution unit installed in the reaction tank, into which returned sludge from the precipitating tank is introduced, in which a separate reaction from a reaction in the reaction tank is carried out to elute a chemical from reactants and unreacted chemicals contained in the returned sludge, and from which the eluted chemical is introduced into the reaction tank.
According to this invention, fluorine contained in wastewater can be treated in the recycling tank having the precipitation section while recycling ingredients in the returned sludge. Furthermore, reactants and unreacted chemicals can be eluted from the returned sludge in the elution unit installed in the reaction tank and reused for wastewater treatment.
Hydrogen peroxide contained in fluorine wastewater can be treated by anaerobic microorganisms having reducibility propagated in the recycling tank into which the returned sludge is introduced. Since the precipitating tank and the recycling tank are maintained in an anaerobic state, anaerobic microorganisms are propagated in the returned sludge with the passage of time. Thus, hydrogen peroxide can be treated by anaerobic microorganisms having reducibility.
Organic matter in the wastewater can be treated by anaerobic microorganisms propagated in the recycling tank into which the returned sludge is introduced.
The present invention still further provides a wastewater treatment equipment for treatment of fluorine wastewater which contains hydrogen peroxide or organic matter, comprising: an acid raw water tank; a recycling tank having a precipitation section, to which returned sludge is introduced; a reaction tank; a first polymer coagulant coagulating tank; a first precipitating tank from which sludge is returned to the recycling tank; a poly aluminium chloride coagulating tank; a second polymer coagulant coagulating tank; a second precipitating tank; and an elution unit installed in the reaction tank, into which returned sludge from the second precipitating tank is introduced, in which a separate reaction from the reaction in the reaction tank is carried out to elute a chemical from reactants and unreacted chemicals contained in the returned sludge, and from which the eluted chemical is introduced into the reaction tank.
According to this invention, fluorine can be highly treated in a stable manner since fluorine contained in the wastewater is treated by two-stage coagulo-precipitation by using the recycling tank, the reaction tank, and the first polymer coagulant coagulating tank and the poly aluminium chloride coagulating tank and the second polymer coagulant coagulating tank.
Since aluminium hydroxide sludge is returned from the second precipitating tank to the separate reaction unit in the interior of the reaction tank, aluminium hydroxide can be reused to reduce the consumption of poly aluminium chloride. Also, since sludge containing unreacted calcium hydroxide is returned from the first precipitating tank to the recycling tank, unreacted calcium hydroxide can be reused to reduce consumption of calcium hydroxide.
Hydrogen peroxide contained in fluorine wastewater can be treated by anaerobic microorganisms having reducibility propagated in the recycling tank having the precipitation section into which the returned sludge is introduced.
Organic matter contained in fluorine wastewater can be treated by anaerobic microorganisms having reducibility propagated in the recycling tank having the precipitation section into which the returned sludge is introduced.